Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$173.76	6.408%	$184.8945	$184.89	$184.90	$184.90
Purchase #2	$173.95	5.672%	$183.8164	$183.82	$183.80	$183.80
Purchase #3	$133.35	7.105%	$142.8245	$142.82	$142.80	$142.80
Purchase #4	$70.45	4.212%	$73.4174	$73.42	$73.40	$73.40
Purchase #5	$55.98	11.754%	$62.5599	$62.56	$62.55	$62.60
Purchase #6	$238.86	13.595%	$271.333	$271.33	$271.35	$271.30
Purchase #7	$169.46	3.383%	$175.1928	$175.19	$175.20	$175.20
7 purchase totals =	$1,015.81		$1,094.0385	$1,094.03	$1,094.00	$1,094.00